You are not using a header
Menu transparency works if you have applied to your page a header: Basic Header, Uncode Content Block or Slider Revolution plugin. If you create only a row of contents this is not interpreted by Uncode as a header and not special functionalities will be available. Please be sure you have connected to your page a header with the Theme Options or Page Options. You can find more info in the Headers Section or in the Faq section Where is the header?
You have deactivated from Theme Options
Be sure you have not selected the option to remove the transparent menu from the Theme Options. For example, this screenshot refers to the Page type but you have also selective for all the page/post typology.
Your menu background color is not transparent
In Theme Options → Customize → Light and Dark Skins, you have not set a transparent or semi-transparent value for the Primary Menu Background Opacity option.
You have removed from the Page Options
Inside your Page Options, at the very bottom of your page, at the tab Menu, you have checked the Remove Transparency option.
You are using LayerSlider (prior to Uncode 1.7.5)
In versions prior to Uncode 1.7.5 was not possible to have a transparent menu and automatic skins color changes with the LayerSlider plugin and Uncode as you have if you work with the native Basic Header, the native Uncode Content Block or the extra Slider Revolution plugin. If you need to have a transparent menu with LayerSlider please be sure to have installed at least Uncode 1.7.5.